The invention relates to an RF coil system for a magnetic resonance imaging apparatus and to a magnetic resonance imaging apparatus of this kind.
Magnetic resonance imaging (MRI) apparatus is used notably for the examination and treatment of patients. The nuclear spins of the tissue to be examined are then aligned by means of a basic magnetic field and excited by RF pulses. The RF relaxation processes thus induced are subjected to gradient magnetic fields and are received and processed so as to form an image of the examination zone.
A distinction can be made between the so-called open MR systems (vertical systems) in which a patient is introduced into an examination zone which is situated between the ends of a C-arm so that the patient is accessible from practically all sides during the examination or treatment, and MR systems which comprise a tubular examination zone (axial systems) in which the patient is introduced. These differences also necessitate completely different arrangements and configurations of the devices whereby the basic magnetic field, the gradient magnetic fields and the RF signals are generated and received.
The transmission and reception of the RF signals necessitates the use of RF coil systems whose configuration and position have a decisive effect on the image quality, that is, on the signal-to-noise ratio and the resolution in particular. In addition to the RF coil systems which are permanently mounted in the system, use is made of so-called RF body coils which can be flexibly arranged, for example, as sleeves or pads, around or on the zone to be examined.
Not only the type of MR apparatus but notably also various patient data such as the size of the patient as well as the type, position, depth and dimensions of the zone (organ) to be examined and any motions in this zone etc. are of decisive importance for the optimization or selection of the RF coil systems. Therefore, at the beginning of an examination the user generally has to carry out test exposures by means of RF coils of different size and in different position so as to achieve an optimum image of the zone to be examined. This procedure may be very time-consuming, the more so when the patient must be moved out of the MR apparatus a number of times. This is the case notably when an axial system is concerned.
In order to avoid this problem, for example, from DE 40 30 878 it is known to utilize a double surface coil with two single coils which can be activated, via switches, either individually or in combination so as to achieve an optimum image quality.